1. Technical Field
The present invention relates to a control technology of a rotary drive motor equipped in an image forming apparatus.
2. Related Art
There has been known an image forming apparatus that forms a full-color polychromatic image by forming an electrostatic latent image on a charged photoconductor, then rotating a rotary whose rotation axis is disposed with a plurality of developing cartridges (so-called “toner cartridges”) storing color toners for respective colors for color printing, and forming a toner image on the photoconductor by sequentially switching developing positions of the rotary (so-called “four-cycle system”). Such an image forming apparatus of the four-cycle system is disclosed in, for example, JP-A-2004-109321.
Incidentally, in the existing image forming apparatuses of the four-cycle system, the drive motor of the rotary is driven at a constant torque. At this moment, in the case where the torque of the drive motor is conformed to the maximum torque required for rotating the rotary, minute vibration occurs when the required torque is small, causing large operation noise and thereby bringing discomfort to a user. On the other hand, if the torque is reduced in order to minimize the noise, loss of synchronism occurs when the required torque is large, whereby development cannot be performed because a rotary developing unit cannot be rotated to the developing position, causing image degradation.
For this reason, in order to reduce the noise caused when rotating the rotary, there has been adopted a control method for slowly rotating the rotary after conforming the torque of the drive motor to the maximum torque required for rotating the rotary. According to this control method, the occurrence of loss of synchronism can be prevented and at the same time the noise can be reduced. However, it takes a long time to switch the developing cartridges, slowing the print speed and causing another stress to the user.